nomainwin
WindowWidth=400:WindowHeight=400
open "Draw a Triangle" for graphics_nsb_nf as #1
#1 "trapclose [quit]"
#1 "down; fill cyan"
#1 "color red; size 5"  'will be used to outline figure
#1 "backcolor yellow"   'will be used to fill figure
#1 "setfocus;when leftButtonDown [draw]"
#1 "place 10 30"
#1 "\Click three spots to draw a triangle."

h=hwnd(#1)  'window handle

'get device context for window:
calldll #user32, "GetDC",_
h as long,_ 'window handle
hdc as long 'returns handle to device context

STRUCT PolyPoints,_
    x1 as long,_
    y1 as long,_
    x2 as long,_
    y2 as long,_
    x3 as long,_
    y3 as long
nCount=3   'number of x,y pairs in STRUCT

wait

[draw]
    count=count+1
    if count=1 then
        'remove text
        #1 "fill cyan"
        'draw vertex
        #1 "set ";MouseX;" ";MouseY
        'fill first xy pair in struct with mouse coords
        PolyPoints.x1.struct=MouseX
        PolyPoints.y1.struct=MouseY
        wait
    end if

    if count=2 then
        'draw vertex
        #1 "set ";MouseX;" ";MouseY
        'fill second xy pair in struct with mouse coords
        PolyPoints.x2.struct=MouseX
        PolyPoints.y2.struct=MouseY
        wait
    end if

    if count=3 then
        'draw vertex
        #1 "set ";MouseX;" ";MouseY
        'fill struct with last point xy
        PolyPoints.x3.struct=MouseX
        PolyPoints.y3.struct=MouseY
        count=0 'reset counter variable
    end if

    'after the third mouse click, draw the triangle
    calldll #gdi32, "Polygon",_
    hdc as long,_         'device context of window or control
    PolyPoints as struct,_'array of points
    nCount as long,_      'number of x,y pairs in array
    result as boolean

    'method to flush GDI graphics:
    #1 "place 10 30"
    #1 "\Click three spots to draw a triangle."
    #1 "segment segID"
    #1 "delsegment segID"
    #1 "getbmp pix 0 0 400 400"
    #1 "drawbmp pix 0 0;flush"

    wait

[quit]
close #1

calldll #user32, "ReleaseDC",_
h as long,_     'window handle
hdc as long,_   'device context
ret as long

end